Coking expanding coals



April 1s, 195o Filed Feb. 18, 1947 PRESSUEEf POUNDS PE2 SQUARE. INCH M.PERcH 25045150 COKING EXPANDING GOALS 2 Sheets-Sheet 2 La? 9 Wl fao e Vr 7 /l 5 l l/./ 4 /I/ 3 2 f56 Z .b 4 .J 6 7 9 HOURS AFTER CHARGINGSlwcntor mzcHAEL Psecf/ I Cittorneg Patented Apr. 18, 1950 COKINGEXPANDING COALS Michael Perch, North Arlington, N. J., signor to KappersCompany, Inc., Pittsburgh, Pa., a corporation oi Delaware ApplicationFebruary 18, 1947, Serial No. 729,328

3 Claims. l

The present invention relates to the coking oi' coals in by-product cokeovens, and has reference more particularly to novel procedure for theutilization of expanding coals and expanding coal mixtures in such cokeovens.

The problems encountered by the expansion of coal during coking has longbeen known in the industry and has been subjected to much study in aneffort to alleviate the condition. The development of the modernhorizontally elongated coke oven and oi' high temperature coking, andthe enhanced productive capacity of coke ovens obtainable thereby, hasincreased the importance of the problem since such higher rates ofcoking develop higher expansion pressures within the oven.

Coals and coal mixtures are considered expanding if they exert, duringthe process of coking, such pressuresagainst the walls of the ovenchamber that they either damage the oven ,walls or affect deleteriouslytheir useful life. On the basis of their experience, coke-oven operatorshave in general arbitrarily set an expansion pressure of two pounds persquare inch as the highest pressure permissible against coke oven walls.

Methods for reducing coal expansion pressures by altering the physicaland general characteristics of the selected coal and coal mixtures havebeen uniformly unsuccessful because they also deleteriously aii'ect thequality of the coke produced therefrom. A recent method, disclosed andclaimed in copending application of Powell, Serial No. 612,160, providesa means for reducing to within safe limits the final expansion pressuresof coals which expand during the latter part of their coking period, atwhich time, it is believed. the plastic seams produced in the coalduring coking join to form a continuous plastic envelope which entrapsthereinpressure producing gases. The Powell method substantiallyprevents the closure of the plastic seams. However, the expandingcharacteristic of some coals and coal mixturesl is so pronounced thatgreatly excessive pressures may develop during the first period ofcoking when the Powell method is ineffective to reduce expansionpressures.

The primary object of the present invention is .the provision of amethod whereby highly expanding coals and coal mixtures can be coked atcustomary. high temperatures in the usual byproduct coke ovens withoutdamage to the ovens other operative advantages or results as may befound to obtain in the processes or apparatus hereinafter described orclaimed.

According to the present invention, expanding coal or expanding coalmixtures are admixed with a minor quantity of pitch and there isdisposed along any surface of an oven charge constituting such anadmixture a stratum of solid fuel that is itself either non-coking ornon-agglomerating or forms during coking a weak, gas permeable plasticseam. The striking eifect of the described combination in the reductionof the expansion of highly expanding coals is particularly surprisinginasmuch as the use of either pitch admixture alone or of the stratumalone provides no appreciable reduction in the expansion of these coals.The stratum can constitute an entire and uniform layer in the plane ofone surface of the coal charge, or it can be a series of broken layersconstituting only a portion of any particular plane of the charge, or itcan be a single layer not entirely covering one surface of the charge.or it may be one or more layers in one or more heating planes of theoven charge. The stratum or layer can consist of any inert non-cokingmaterial through which gases can readily permeate, especially coke, ofwhich one preferred example is breeze. oxidized coal is another suitablenon-coking material.

The pitch can be a mineral pitch or a coal tar pitch, such as roofingpitch or fuel pitch, the latter being preferred because it isconsiderably less expensive. Suitable coal tar pitch is defined in theStandards of the ASTM, Part II, page 612, (1944) as Black or dark-brownsolid cementitious residues which gradually liquefy when heated andwhich are produced by the partial evaporation or fractional distillationof tars. The aforesaid preferred coke breeze which may be used for thepresent coking method is defined in the Standards of the ASTM, Part III,page 61, (1944) as follows: The iine screenings from crushed coke orfrom coke as taken from the ovens, of a size varying in local practicebut usually passing a 1/2 inch or inch screen opening. The successfuloperation of the present invention is of course not restricted toemployment of the defined coke size. Particulate coke of larger sizesand mixed sizes arealso. effective in the combination of this invention.It is obviously necessary to avoid coke pieces too large to enter thecharging hole without diiliculty, or so large that the void spacesbetween them would permit radiation of heat through the stratum and forma, plastic seam at the underlying coal surface.

Dangerous expansion-pressures have been defined arbitrarily by thoseexperienced in cokeoven operation as those which exceed a pressure oftwo'pounds per square inch on the oven walls.

coking are measured in standard test ovens.

The apparatus that was employed in the hereinafter reported tests is themovable-wall oven illustrated and described in Proceedings of the ASTM43, p. 310 (1943). Pressures exerted by coking coals below the saidlimit are identified in the claims as pressures of a normal value andmbelievedtobebeneiicialandtobeanim portant factor in the production of ahigh quality coke having stable physical characteristics.

In the accompanying drawings forming a part of the speciilcation,

Fig. 1 is a fragmental, elevational view in vertical section ofcoke-oven chambers and their accompanying dues and crossovers takenlongitudinally of the coke-oven battery and at right angles to thehorizontal extension of the individual ovens, and showing one oven ascharged and another oven at an intermediate period during coking, andillustrating a` stratum of coke at the top of the ovens to prevent, incombination with admixed pitch, the development of high pressure in theoven,

Pig. 2 shows curves with coal expansion pressures plotted against cokingtime of an expanding coal, which was coked according to standardpractice in one instance, with admixed pitch only in another, and with asuperimposed layer of breeze in another, and

Figs. 3 and 4 are curves showing coal expansion pressures plottedagainst coking time of the same expanding coal which was coked accordingto the method of invention. Y

Referring now to the drawings, Fig. 1 illustrates a preferred embodimentof the invention whereby a highly expanding coal, admixed with pitch, iscoked without exerting excessive expansion pressures. In this instance,after levelling, a layer of coke breeze is added to an oven chargecomprising expanding coal and a 'minor quantity of coal-tar pitch. Alayer of breeze approximately no greater in thickness than the width ofoven chamber is formed across the top of the ovenV charge. Fig. 1 showstwo oven chambers, one chamber 2, which is represented as just havingbeen charged, and an adjacent oven chamber 4, in which the oven chargeis partially coked. Each chamber is formed by two longitudinallyextending flued, masonry walls B, and an oven sole 8 and a masonry roofIU. The ovens are also supplied with regenerators I2, air and waste heatports I4 and I6, respectively. and with fuel gasburner nozzles I8.

As is the well known process in the heating of reversible regenerativecoke ovens, air is passed through checkerwork in the said regenerator I2and is flowed therefrom through air ports I4 into "on" flues 20 whereinthe air intermingles with, and burns fuel gas introduced through thesaid burner nozzles I8. The burning mixed gases iiow through crossoverducts 22 and descend on the opposite side of an oven chamber through an"oil" flue' 2B. The waste heat ows from the latter flue through ducts I8into another set of regenerators I2 to preheat the checkerbrickcontained therein.

The described technology of coking coal in horizontal coke ovens of animproved design provide uniformity of heating and the delivery of heatfrom all sides of the oven chamber, thus causing the formation of thedescribed plastic envelope. In addition, highly expanding coals formhighly viscous plastic seams which themselves exert considerableexpansion pressures.

A' completely sealed, uninterrupted plastic envelopc surrounding andenclosing the central portion of the coal-charge cannot be formed 4when, as illustrated in Fig. 1, a non-coking fuel Is positioned asslayer 24 adjacent and between heating walls, jbecause no plastic seamcan be formed in the non-coking fuel, and because the layer insulatesthe underlying surface of the coal `charge from heat which otherwisewould be radiated from the adjacent heating wall. A layer of coke breezeis particularly eiective to permit escape of gases from the underlyingcoke charge, for the said breeze is substantially. uninuenced by thecoking heat. The layer 24 of coke breeze can be introduced into the ovenchamber through charging holes 26 after the oven has been charged withcoal.

The hereinbefore described viscous and pressure exerting plastic seam ofhighly expanding coal appears to be altered by the admixture with thecoal of minor quantities of pitch and, hence, a plastic seam 28 as shownin Fig. 1 represents a seam which has been so altered by the pitchaddition that it in itself develops only minor expansion pressures.

The layer 24 which is disposed on the top of the charge in each of theoven chambers can also constitute coke pieces of larger size thanbreeze, or may be coke of mixed sizes.

Fig. 2 illustrates by curves the expansion pressures developed duringthe coking of 1) a highly expanding low-volatile coal (curve 30), (2)the same coal to which has been added 10% by weight of the coal ofcoal-tar pitch '(curve 32), and (3) the same coal upon the upper surfaceof an voven charge of which a 7" deep layer of coltev breeze has beenaddedI (curve 34). It can be seen from the curves that neither theexpedient of admixed pitch nor of a stratum of a solid fuel is effectivealone to reduce the expansion pressures of highly expanding coals. Arealization of the extremely dangerous pressures exerted by this coalwill be had when the line 35, indicatingthe arbitrarily set limit forsafe coal expansion, is noted on the figure.

Figs. 3 and 4 illustrate the expansion curves exhibited by the sameexpanding coal when it has been admixed with pitch and protective solidfuel stratum has been distributed over the top of the oven charge. Asshown, the greatly excessive expansion pressures to be observed in Fig.2 have been completely eliminated and, instead, there remains onlymoderate pressures well within the limit of 2 lbs. per sq. in., andVconducive to the production of high quality coke.

The data and test conditions from which the results reported by thedescribed curves were obtained are given in the following specificexamples.

Example 1 An expanding coal was selected, which had the followingpulverization:

Per cent by weight On 41" screen 0.5 Through 1A," and on t/a" screen11.8 Through 1/8" and on 11g" screen 46.6 Through 1*," screen 41.1

The coal had a bulk density of 49.7 lbs. per cu. ft. and a moisture of1.5% by weight. When coal was coked for about 81/2 hours in theaforementioned movable wall oven which had an average ue temperature of2473 F., a maxi" mum pressure of 10.1 lbs. per sq. in. was developed.The expansion-pressure curve is shown as curve 30 of Fis. 2.

Example 2 The'same coal as was used in Example 1, but having a slightlyhigher bulk density. 52.6 lbs. per cu. ft., due perhaps to its lowermoisture con-- tent of less than 1%, was coked in the aforesaid movablewall oven which had during the test an average nue temperature -of 2453F. A layer of coke breeze 7 deep was distributed over the top of theoven charge immediately after charging. The expansion pressure that wasdeveloped exceeded the limit of the apparatus at 11.9 lbs. per sq. in.The curve 34 of Fig. 2 illustrates the expansion pressure developed bythis example.

Example 3 The same expanding low volatile coal as was employed inExample 'l and having a moisture content of less than 1% and a bulkdensity of 51.4 lbs. per sq. in. was mixed with 10% by weight ofcoal-tar pitch. The admixture was coked in the aforesaid movable walloven and the expansion pressure exceeded the limit of the apparatus at11.5 lbs. per sq. in.

The expansion pressures observed during this test are illustrated incurve 32 of Fig. 2. From the foregoing specific examples it can be seenthat a highly expanding coal cannot be effectively treated forelimination of excessive expansion pressures by admixing pitch alone orby providing a protective stratum of solid fuel against one of thesurfaces of the coal charge without admixture with pitch.

The remarkable and unexpected effect o1 the A use of pitch and theprotective stratum in com bination is shown in the following examples.

Example 4 The said low volatile coal, having a bulk density oi 50 lbs.per cu. ft. and moisture of less than 1% and a pulverization of 93.3%through a 1/8" screen, was mixedwith 10% by Weight of coal-tar pitch.The admixture was charged to the aforesaid movable wall oven and a layerof coke breeze`7 deep was added to the top of the charge. vThe chargewas coked at an average ue temperature of 2462 F. and exhibited amaximum coal expansion pressure of 1.29 lbs. per sq. in. The cokeproduced was of ysuperior quality. The coal expansion pressuresexhibited during this test are illustrated in Fig. 3.

Example The said coal having a bulk density of 47 lbs. per cu. ft., amoisture of 1%, and a pulverization of 86.9% through a 1;/8" screen wasmixed with by weight of coal-tar pitch. The admixture was charged intothe aforesaid movable wall oven and a layer o1 coke breeze 10" deep wasadded to the top of the charge. The charge was coked for approximately 8hours at an average flue temperature of 2495 F. and a maximum expansionpressure of 0.7 1b. per sq. in. was recorded. Fig. 4 illustrates theexpansion pressures observed in this test.

Example 6 Another low volatile coal which. when coked alone, exhibits anexcessively dangerous coal expansion pressure of a degree equal to thecoal used in the above specific examples was coked in admixture with 10%ot fuel pitch and with a layer of breeze 8" deep on the coal charge. Amaximum expansion pressure of 1.82 lbs. per sq. in. was recorded.

Example 7 7.5% by weight o1' pitch was mixed with the coal used inExample 1 and was coked with an 8" layer of breeze thereon as an upperlayer. For this particular coal having extremely expandingcharacteristics the use of 7.5% of pitch appears to be the minimumproportion providing a safe expansion pressure because a maximumexpansion pressure of 2.17 lbs. per sq. in. was produced in this exampleand the test was performed under conditions which produce the highestobtainable coking pressures.

Example 8 The coal employed in Example 1 was mixed with 10% by weight ofcoal-tar pitch and was coked with a superimposed six-inch layer of cokebreeze. The maximum expansion pressure-exhibited was slightly over 2lbs.v per sq. in. and consequently this appears to be a lower limit ofthickness which will provide safe coking pressures when one uses theaforesaid highly expanding coal in admixture withv 10% of pitch and whenthe protective layer vconstitutes coke breeze.

The extremely expanding nature of the coals selected for the abovetesting causes the reported results to establish thereby thesubstantially ultimate limits in respect of the minimum of pitch to beadded and minimum thickness of protective layer to be employed for anyexpanding coal. It is obviously within the skill of the art to determinethe expansion pressure exhibited by any untreated coal or coal mixtureand to 'add a correct proportion of pitch and a correct depth oi' a-protective layer.

The expansion pressure exhibited by a selected coal or coal mixtureincreases with increase in coking temperature and therefore the problemhereinbefore described of excessive expansion pressures is most pressingwhen the high temperatures of modern coking practice are employed.However, it is clearly within the scope of the present invention toemploy the elements of the disclosed combination in lesser proportionzvhen it is preferred to use lower coking temperaures.

Although in the hereinbefore described Fig. 1 the stratum thereillustrated is shown to be rectangular in cross section, the stratum ofinvention need not be so and equally good results have been obtainedwhen the stratum was triangular in cross section with the apex pointingdown or, in another instance, when the cross section of the stratumroughly conformed to the cross sec- 'tion of an inverted truncated cone.

The invention as hereinbeforeset forth is embodied in particular formand manner but may be variously embodied within thev scope of the claimshereinafter made.

I claim:

l. In a method of carbonizing coal in an externally heated horizontallyelongated coke oven having sidewalls which are susceptibleoi' injurywhen subjected to pressure in excess of 2 lbs. per square inch, themethod of preventing injury to the side walls during carbonization of anexpanding coal of the type which when carbonized in an oven in the usualmanner has created therein said expanding coal to nll a major portion ofthe oven, mixing pitch with the coal charge in the amount ofsubstantially 7.5 to by weight oi the coal charge to reduce swelling ofthe plastic zone, driving heat through the opposite sides oi the coalbody to make it plastic and coke it within the temperature rangefor hightemperature coking, and providing during the carbonization period acovering for a surface of the coal body coni sisting of a porous layerof granular material of such composition and thickness as to provide astructure of the coal being carbonized and the material thereon topermit the ready escape therethrough of gas generated by the coalcarbonization without .developing a pressure in excess of 2 lbs. persquare inch against the oven walls during the coking period.

2. In a process of carbonizing coal Ain an externally-heatedhorizontally-elongated intermittent coke oven having sidewalls which aresussubstantially uninterrupted highly impermeable plastic zonesurrounding and enclosing the central portion of the coal-charge andwhich when carbonized in the usual manner also causes pressures inexcess of said normal value to be exerted againstthe oven side wallsduring a substantial part of the carbonizing period prior to the latterpart of the carbonizing period because of the swelling of the plasticzones in the coal-charge, y

said method comprising charging said oven with coal of the typeidentified above and to which there has been added pitch in the amountof substantially 7.5 to 10% of the weight of the coalcharge to therebyreduce the swelling of the plastic zones in said coal-charge to such adegree as to prevent pressures in excess of said normal value beingexerted against the oven side walls prior to the latter part of thecarbonizing period, and preventing the formation in said coal-chargeduring the latter part of the carbonizing period of an uninterruptedhighly impermeable plastic zone by providing over at least a substantialpart of the above-identified coal-charge a porous layer of granularmaterial of such composition that a highly impermeable plastic zone doesnot develop within said layer as a result of exposure of said layer tothe temperatures encountered in said oven and of such thickness as toprevent heat radiated from the roof of said oven and from the uperportion of the side walls of said oven from developing a highlyimpermeable plastic zone across the top of said coal-charge.

3. A method of carbonizing in an externallyheated horizontally-elongatedintermittent coke oven having side walls which are susceptible of injurywhen subjected to pressure in excess of a normal value coal of a typewhich when carbonized in the usual manner causes pressures in excess ofsaid normal value to be exerted against the oven side walls during thelatter part oi the `carbonizing period because oi. the formation duringthe latter part of the carbonizing period oi a substantiallyun-interrupted highly impermeable plastic zone surrounding and enclosingthe central portion of the coal-charge and which when carbonized in theusual manner also causes pressures in excess of said normal value to beexerted against the oven -side walls during a substantial part of thecarbonizing period prior to the latter part of the earbonizing periodbecause of the swelling of the plastic zones in the coal-charge,

said method comprising charging said oven with coal oi the typeidentiiled above and to which has been added pitchin the amount of atleast '1.5% of the weight of the coal-charge to thereby reduce theswelling of the plastic zones in said coalcharge to such a degree as toprevent pressures in excess of such normal values being exerted againstthe oven side walls prior to the latter part4 of the carbonizing period,and preventing the formation in said coal-charge during the latter partofA the carbonizing period of an uninterrupted A coal-charge thematerial of said covering layer remains substantially more permeable togases emitted from said coal-charge than the plastic zone formed in saidcoal-charge, said covering layer being of such thickness as to preventheat radiated from the roof of said oven and from the upper portions ofthe side walls of said oven from developing in the upper portion of saidcoalcharge a plastic zone which can cooperate with the plastic zonesdeveloped in the lower portions of said coal-charge to restrict theescape of gases from the portion of the coal-charge within said plasticzone, whereby the gases evolved from the central portion of saidcoal-charge during carbonization of said coal-charge may readily escapewithout building up to pressures which cause said coal-charge to exertpressures in excess of said normal value on the side walls of said oven.

MICHAEL PERCH.

REFERENCES CITED The following references are of record in the ille ofthis patent:

UNITED STATES PATENTS Number Name Date 955,970 Korting Apr. 26, 19101,268,628 Rusby et al. June 4, 1918 1,512,577 Blythe Oct. 21, 19241,593,208 Culmer July 20, 1926 2,018,664 Fitz et al. Oct. 29, 19352,382,809 Otto Aug. 14, 1945 FOREIGN PATENTS A Number Country Date v322,341 Great Britain C. A. Dec. 5, 1929 842,550 France Aug. 24. 1938

